A method for electroless plating of nickel-palladium-gold on an alumina high-temperature co-fired ceramic substrate

Abstract

The application discloses a method for electroless nickel-palladium-gold plating on an alumina high-temperature co-fired ceramic substrate, and belongs to the technical field of electroless nickel-palladium-gold plating. The method comprises the following steps: hanging, oil removal, micro-etching, glass micro-etching, acid pickling, palladium activation, inhibition, electroless nickel-boron plating, pre-plating of palladium, electroless palladium plating and electroless gold plating. The method is used for electroless nickel-palladium-gold plating on an alumina high-temperature ceramic tungsten metal to modify the metal, so that the workpiece has good weldability and bondability, the gold wire bonding strength can reach 280 mN, the average gold ribbon bonding tension is greater than 500 mN, and the average chip shear strength reaches 5.11 Kgf, all of which reach the relevant technical standards of the national military standard.

Description

Technical Field

[0001] This invention relates to the field of electroless nickel-palladium-gold plating technology, and more particularly to a method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate. Background Technology

[0002] High-temperature co-fired (HTCC) ceramics made of alumina are the most common type of high-temperature co-fired ceramics. The surface of HTCC ceramics features complex tungsten metal patterns. Since tungsten metal itself lacks solderability and bonding properties, the tungsten metal pattern areas on the surface need to be modified to facilitate electronic assembly. Electroless nickel-palladium plating is currently the most common and ideal method for this modification. By modifying the tungsten surface with electroless nickel-palladium plating, the HTCC ceramic substrate acquires good solderability and bonding properties.

[0003] Currently, there are many related reports. For example, Chinese patent CN 114086162 A, "A production line and process for electroless nickel-palladium-gold plating on tungsten-based and tungsten alloy substrates," discloses a method for electroless nickel-palladium-gold plating on tungsten substrates. Another example is Chinese patent CN 115417696 A, "A surface electroplating process for tungsten layers on alumina products," which also discloses a method for electroplating nickel-palladium on the surface of tungsten layers. Yet another example is Chinese patent application CN 110724940 A, "A process for electroless nickel-palladium-gold plating on low-temperature co-fired ceramic substrates," which discloses a method for electroless nickel-palladium-gold plating on LTCC substrates. This process, which uses palladium sulfate for activation, cannot achieve electroless plating on substrates with dense circuitry, and will result in plating penetration.

[0004] Existing methods cannot achieve tungsten metallization with nickel-palladium plating on HTCC alumina ceramic materials. Summary of the Invention

[0005] The purpose of this invention is to provide a method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate, so as to solve the above-mentioned problems.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate, comprising the following steps:

[0007] (1) Hanging: Hanging the workpiece to be processed;

[0008] (2) Degreasing: Degreasing is performed by adding a degreasing agent;

[0009] (3) Double water wash: Perform overflow double water wash to remove residual pretreatment solution from the surface of the workpiece;

[0010] (4) Micro-etching: The workpiece is placed in a micro-etching solution for micro-etching;

[0011] (5) Double water wash: Perform overflow double water wash to remove residual micro-etching solution from the surface of the workpiece;

[0012] (6) Glass micro-etching: The workpiece is placed in NH4HF2 solution for glass micro-etching;

[0013] (7) Double water wash: Perform overflow double water wash to remove residual glass micro-etching solution from the surface of the workpiece;

[0014] (8) Pickling: Immerse the workpiece in the pickling solution for pickling;

[0015] (9) Palladium activation: Palladium activator is used to activate the tungsten metal and form a layer of metallic palladium on the surface of the tungsten metal;

[0016] (10) Double water wash: Perform overflow double water wash to remove residual palladium activation solution from the surface of the workpiece;

[0017] (11) Inhibition treatment: The workpiece is placed in an inhibition solution for inhibition treatment; the purpose of inhibition is to remove palladium ions that are difficult to wash off by water on the ceramic surface of the workpiece, and to prevent plating penetration.

[0018] (12) Double water wash: Perform overflow double water wash to remove residual inhibitory solution from the surface of the workpiece;

[0019] (13) Electroless nickel-boron plating: The workpiece is placed in an electroless nickel-boron solution for electroless nickel-boron plating;

[0020] (14) Double water rinse: Perform overflow double water rinse to remove residual chemical nickel plating solution from the surface of the workpiece;

[0021] (15) Palladium pre-plating: The workpiece is placed in a chemical palladium pre-plating solution for palladium pre-plating;

[0022] (16) Electroless palladium plating: The workpiece is placed in an electroless palladium plating solution for electroless palladium plating;

[0023] (17) Double water wash: Perform overflow double water wash to remove residual chemical palladium plating solution from the surface of the workpiece;

[0024] (18) Chemical gold plating: The workpiece is placed in a chemical gold plating solution for chemical gold plating;

[0025] (19) Double water rinse: Perform overflow double water rinse to remove residual chemical gold plating solution from the surface of the workpiece;

[0026] (20) Water washing; preferably ultrasonic water washing, to better remove residual solution from the surface of the workpiece;

[0027] (21) Drying, preferably at 70-90℃.

[0028] This invention employs a chemical nickel-palladium-gold plating method using nickel-boron plating, which offers better solderability compared to nickel-phosphorus plating. The invention utilizes a special activating solution and a glass micro-etching step to be suitable for tungsten metallization nickel-palladium-gold plating on HTCC alumina ceramics. Furthermore, for substrates with densely packed circuitry, an additional suppression process is added to prevent plating creep.

[0029] As a preferred technical solution: In step (1), polytetrafluoroethylene hangers are used for hanging to prevent plating solution deposition.

[0030] As a preferred technical solution: in step (2), the concentration of the degreasing agent is 45-55 g / L, the degreasing temperature is 45-55℃, and the degreasing time is 5-10 min.

[0031] As a preferred technical solution: in step (4), the concentration of the micro-etching solution is 300-500 ml / L, the micro-etching temperature is RT~80℃, and the micro-etching time is 20s~30min.

[0032] As a preferred technical solution: in step (6), the concentration of the NH4HF2 solution is 10g to 50g / L, the glass micro-etching temperature is RT, and the glass micro-etching time is 5 to 10min.

[0033] As a preferred technical solution: in step (8), the pickling solution is an HCl solution of 300-800 ml / L, the pickling temperature is RT, and the pickling time is 5-10 min.

[0034] As a preferred technical solution: In step (9), the palladium activator used is: palladium chloride (with a palladium content of 10-30 mg / L), hydrochloric acid 10ml-30ml / L, activation time 3-10min, and activation temperature 60-80℃.

[0035] Through extensive experimentation, the inventors of this application have developed a method using palladium chloride and hydrochloric acid, which is more suitable for production and solves the problems of plating penetration and plating omission when using existing technologies for chemical plating of substrates with dense circuits.

[0036] As a preferred technical solution: in step (9), the concentration of the inhibition solution is 100-150 ml / L, the inhibition treatment temperature is 60-80℃, and the inhibition treatment time is 5-10 min.

[0037] As a preferred technical solution: in step (13), the concentration of the chemical nickel boron solution is 60-65 ml / L, the treatment temperature is 60-65℃, and the treatment time is 10-30 min.

[0038] As a preferred technical solution: In step (15), the chemical composition of the pre-plating palladium solution is TPD-30-MW 25-30ml / L, TPD-30-C 35-40ml / L, dichlorotetraamminepalladium 0.6g-0.7g / L, the temperature is 70~90℃, and the time is 1~5min;

[0039] In step (16), the chemical composition of the palladium plating solution is TPD-30-MW 100-120 ml / L, TPD-30-C 150-200 ml / L, dichlorotetraamminepalladium 0.6-0.7 g / L, the temperature is 40-50℃, and the time is 4-10 min;

[0040] In step (19), the chemical composition of the electroless gold plating solution is TWX-40-M10 100-120ml / L, KCN 50-60ppm / L, KAuCN 1.0-1.2g / L, the temperature is 70~80℃, and the time is 10~30min.

[0041] Compared with the prior art, the advantages of the present invention are as follows:

[0042] This invention modifies the metal by electroless nickel-palladium-gold plating on high-temperature ceramic tungsten metal in alumina, giving the workpiece good solderability and bonding properties. The average gold wire bonding strength can reach 280mN, the average gold strip bonding pull force is greater than 500mN, and the average chip shear strength reaches 5.11Kgf, all of which meet the relevant technical standards of the National Military Standard. This invention solves the problems of plating penetration and incomplete plating after nickel-palladium-gold plating, ensuring the circuit continuity is qualified. Attached Figure Description

[0043] Figure 1 A photograph of the coating obtained in Example 1 of the present invention;

[0044] Figure 2 This is a photograph of the coating obtained in Comparative Example 2 of the present invention;

[0045] Figure 3 This is a photograph of the coating obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0046] The present invention will be further described below with reference to embodiments.

[0047] The reagents in the following examples:

[0048] Degreasing agent: purchased from Uemura Kogyo, brand name C-4000;

[0049] Micro-etching solution: purchased from Uemura Kogyo, brand name KFE300;

[0050] Inhibition solution: purchased from Uemura Kogyo, brand name MPD-BW;

[0051] Chemical nickel-boron solution: purchased from Uemura Kogyo, brand name BEL-18;

[0052] In the chemical pre-plating palladium solution: TPD-30-MW, purchased from Uemura Kogyo; TPD-30-C, purchased from Uemura Kogyo.

[0053] In the chemical gold plating solution: TWX-40-M10 was purchased from Kamimura Kogyo;

[0054] The reagent concentrations used in this application are all based on water as the solvent dosage. For example, "45g / L degreasing agent" means adding 45g of the purchased degreasing agent C-4000 to 1L of water; "300ml / L micro-etching solution" means adding 300ml of the purchased micro-etching solution KFE300 to 1L of water. Example

[0055] A method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate includes the following steps:

[0056] 1. Hanging: Use PTFE racks for hanging to prevent plating solution from depositing;

[0057] 2. Degreasing: Place the product in a degreasing agent at 45 g / L for 5 minutes at 45°C.

[0058] 3. Double water rinse: Perform an overflow double water rinse to remove residual pretreatment solution from the workpiece surface;

[0059] 4. Micro-etching: Immerse the workpiece in a 300ml / L micro-etching solution for micro-etching at a temperature of RT for 20Smin.

[0060] 5. Double water rinse: Perform an overflow double water rinse to remove residual micro-etching solution from the workpiece surface;

[0061] 6. Glass micro-etching: Immerse the workpiece in a 10 g / L NH4HF2 solution at a temperature of RT for 5 min.

[0062] 7. Double water rinse: Perform an overflow double water rinse to remove residual glass micro-etching solution from the surface of the workpiece;

[0063] 8. Pickling: Immerse the workpiece in a 300 L / L HCl solution at a temperature of RT for 5 minutes;

[0064] 9. Palladium activation: Palladium activator: 10 mg / L palladium, 10 ml / L hydrochloric acid, activation time 3 min, temperature 60℃, to form a layer of metallic palladium on the tungsten metal surface;

[0065] 10. Double water rinse: Perform an overflow double water rinse to remove residual palladium activation solution from the surface of the workpiece;

[0066] 11. Suppression: The spacing between the tungsten metal workpieces in this embodiment is relatively large (greater than 5mm), so the suppression step is omitted;

[0067] It should be noted that, by suppressing the plating process, this invention can prevent plating creep from occurring on substrates with very dense circuits (generally referring to a spacing of less than 5 mm) after plating. However, for substrates with sparse circuits (where the tungsten metal spacing is relatively far apart), suppression is not necessary.

[0068] 12. Double water rinse: Perform an overflow double water rinse to remove residual inhibitory solution from the workpiece surface;

[0069] 13. Electroless nickel-boron plating: Immerse the workpiece in a 60ml / L electroless nickel-boron solution at 60℃ for 10 minutes;

[0070] 14. Double water rinse: Perform an overflow double water rinse to remove residual chemical nickel plating solution from the surface of the workpiece;

[0071] 15. Palladium pre-plating: Immerse the workpiece in a chemical palladium pre-plating solution (TPD-30-MW 25ml / L, TPD-30-C 37.5ml / L, dichlorotetraamminepalladium 0.6g / L) at 70℃ for 1 minute;

[0072] 16. Electroless palladium plating: Immerse the workpiece in an electroless palladium plating solution (TPD-30-MW 100ml / L, TPD-30-C 150ml / L, dichlorotetraamminepalladium 0.6g / L) at 40℃ for 4 minutes;

[0073] 17. Double water rinse: Perform an overflow double water rinse to remove residual chemical palladium plating solution from the surface of the workpiece;

[0074] 18. Chemical gold plating: Immerse the workpiece in a chemical gold plating solution (TWX-40-M10 100ml / L, KCN 50ppm / L, KAuCN 1.0g / L) at 70℃ for 10 minutes.

[0075] 19. Double water rinse: Perform an overflow double water rinse to remove residual chemical gold plating solution from the surface of the workpiece;

[0076] 20. Ultrasonic water washing: Ultrasonic water washing is used to better remove residual solution from the surface of the workpiece;

[0077] 21. Drying: Dry at 70℃.

[0078] The resulting workpieces all exhibited a gold wire bonding strength (test method referred to GJB548 Method 2011.1 Condition A) of 285 mN, an average gold strip bonding pull force (test method referred to GJB548 Method 2011.1 Condition A) of 512 mN, and a chip shear strength (test method referred to GJB548 Method 2019.2) of 5.13 kgf.

[0079] The resulting coating is as follows Figure 1 As shown. Example

[0080] A method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate includes the following steps:

[0081] 1. Hanging: Use PTFE racks for hanging to prevent plating solution from depositing;

[0082] 2. Degreasing: Place the product in a degreasing agent at 50g / L for 10 minutes at 55℃.

[0083] 3. Double water rinse: Perform an overflow double water rinse to remove residual pretreatment solution from the workpiece surface;

[0084] 4. Micro-etching: Immerse the workpiece in a 300ml / L micro-etching solution for micro-etching at 80℃ for 30 minutes;

[0085] 5. Double water rinse: Perform an overflow double water rinse to remove residual micro-etching solution from the workpiece surface;

[0086] 6. Glass micro-etching: Immerse the workpiece in a 50 g / L NH4HF2 solution at a temperature of RT for 10 min.

[0087] 7. Double water rinse: Perform an overflow double water rinse to remove residual glass micro-etching solution from the surface of the workpiece;

[0088] 8. Pickling: Immerse the workpiece in 800 ml / L HCl solution at a temperature of RT for 10 min;

[0089] 9. Palladium activation: Palladium activator: 30 mg / L palladium, 30 ml / L hydrochloric acid, activation time 10 min, temperature 60~80℃, to form a layer of metallic palladium on the tungsten metal surface;

[0090] 10. Double water rinse: Perform an overflow double water rinse to remove residual palladium activation solution from the surface of the workpiece;

[0091] 11. Inhibition: Inhibition is to remove palladium ions that are difficult to wash off the ceramic surface of the workpiece by water, and to prevent plating penetration. The workpiece is placed in an inhibition solution of 100 ml / L at a temperature of 80℃ for 10 min.

[0092] 12. Double water rinse: Perform an overflow double water rinse to remove residual inhibitory solution from the workpiece surface;

[0093] 13. Electroless nickel-boron plating: Immerse the workpiece in a 60 ml / L electroless nickel-boron solution at 65°C for 30 minutes.

[0094] 14. Double water rinse: Perform an overflow double water rinse to remove residual chemical nickel plating solution from the surface of the workpiece;

[0095] 15. Palladium pre-plating: Immerse the workpiece in a chemical pre-plating palladium solution (PD-30-MW 25ml / L, TPD-30-C 37.5ml / L, dichlorotetraamminepalladium 0.6g / L) at 90℃ for 5 minutes.

[0096] 16. Electroless palladium plating: Immerse the workpiece in an electroless palladium plating solution (TPD-30-MW 100ml / L, TPD-30-C 150ml / L, dichlorotetraamminepalladium 0.6g / L) at 50℃ for 10 minutes.

[0097] 17. Double water rinse: Perform an overflow double water rinse to remove residual chemical palladium plating solution from the surface of the workpiece;

[0098] 18. Chemical gold plating: Immerse the workpiece in a chemical gold plating solution (TWX-40-M10 100ml / L, KCN 50ppm / L, KAuCN 1.0g / L) at 80℃ for 30 minutes.

[0099] 19. Double water rinse: Perform an overflow double water rinse to remove residual chemical gold plating solution from the surface of the workpiece;

[0100] 20. Ultrasonic water washing: Ultrasonic water washing is used to better remove residual solution from the surface of the workpiece;

[0101] 21. Drying: Dry at 90℃.

[0102] The resulting workpieces exhibit a gold wire bonding strength of 292 mN, an average gold strip bonding tensile force of 517 mN, and a chip shear strength of 5.12 kgf.

[0103] Comparative Example 1

[0104] This comparative example is based on Example 2, except that step "6. Glass micro-etching" is omitted, and the rest is the same as Example 2;

[0105] A method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate includes the following steps:

[0106] 1. Hanging: Use PTFE racks for hanging to prevent plating solution from depositing;

[0107] 2. Degreasing: Place the oil in 50g / L of degreasing agent Shangcun Industrial C-4000 for degreasing at 55℃ for 10min.

[0108] 3. Double water rinse: Perform an overflow double water rinse to remove residual pretreatment solution from the workpiece surface;

[0109] 4. Micro-etching: Immerse the workpiece in the micro-etching solution KFE300 (300 ml / L) for micro-etching at 80℃ for 30 minutes.

[0110] 5. Double water rinse: Perform an overflow double water rinse to remove residual micro-etching solution from the workpiece surface;

[0111] 8. Pickling: Immerse the workpiece in 800 ml / L HCl solution at a temperature of RT for 10 min;

[0112] 9. Palladium activation: Palladium activator: 30 mg / L palladium, 30 ml / L hydrochloric acid, activation time 10 min, temperature 60~80℃, to form a layer of metallic palladium on the tungsten metal surface;

[0113] 10. Double water rinse: Perform an overflow double water rinse to remove residual palladium activation solution from the surface of the workpiece;

[0114] 11. Inhibition: Inhibition is to remove palladium ions that are difficult to wash off the ceramic surface of the workpiece by water, and to prevent plating penetration. The workpiece is placed in the inhibition solution Shangcun Industrial MPD-BW, 100ml / L, at a temperature of 80℃ for 10min.

[0115] 12. Double water rinse: Perform an overflow double water rinse to remove residual inhibitory solution from the workpiece surface;

[0116] 13. Electroless nickel-boron plating: Immerse the workpiece in an electroless nickel-boron plating solution (BEL-18, 60 ml / L) at 65°C for 30 minutes.

[0117] 14. Double water rinse: Perform an overflow double water rinse to remove residual chemical nickel plating solution from the surface of the workpiece;

[0118] 15. Palladium pre-plating: Immerse the workpiece in a chemical pre-plating palladium solution of PD-30-MW 25ml / L, TPD-30-C 37.5ml / L, and dichlorotetraamminepalladium 0.6g / L at 90℃ for 5 minutes.

[0119] 16. Electroless palladium plating: Immerse the workpiece in an electroless palladium plating solution of TPD-30-MW 100ml / L, TPD-30-C 150ml / L, and dichlorotetraamminepalladium 0.6g / L at 50℃ for 10 minutes.

[0120] 17. Double water rinse: Perform an overflow double water rinse to remove residual chemical palladium plating solution from the surface of the workpiece;

[0121] 18. Chemical gold plating: Immerse the workpiece in a chemical gold plating solution of TWX-40-M10 100ml / L, KCN 50ppm / L, KAuCN 1.0g / L at 80℃ for 30 minutes.

[0122] 19. Double water rinse: Perform an overflow double water rinse to remove residual chemical gold plating solution from the surface of the workpiece;

[0123] 20. Ultrasonic water washing: Ultrasonic water washing is used to better remove residual solution from the surface of the workpiece;

[0124] 21. Drying: Dry at 90℃.

[0125] The resulting workpiece blistered during baking at 300℃, resulting in an unqualified coating quality.

[0126] Comparative Example 2

[0127] This comparative example is based on Example 2, except that the palladium activator in step "9. Palladium activation" is replaced with: palladium 30 mg / L and sulfuric acid 30 ml / L, and the rest is the same as in Example 2;

[0128] A method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate includes the following steps:

[0129] 1. Hanging: Use PTFE racks for hanging to prevent plating solution from depositing;

[0130] 2. Degreasing: Place the oil in 50g / L of degreasing agent Shangcun Industrial C-4000 for degreasing at 55℃ for 10min.

[0131] 3. Double water rinse: Perform an overflow double water rinse to remove residual pretreatment solution from the workpiece surface;

[0132] 4. Micro-etching: Immerse the workpiece in the micro-etching solution KFE300 (300 ml / L) for micro-etching at 80℃ for 30 minutes.

[0133] 5. Double water rinse: Perform an overflow double water rinse to remove residual micro-etching solution from the workpiece surface;

[0134] 6. Glass micro-etching: Immerse the workpiece in a 50 g / L NH4HF2 solution at a temperature of RT for 10 min.

[0135] 7. Double water rinse: Perform an overflow double water rinse to remove residual glass micro-etching solution from the surface of the workpiece;

[0136] 8. Pickling: Immerse the workpiece in 800 ml / L HCl solution at a temperature of RT for 10 min;

[0137] 9. Palladium activation: Palladium activator: 30 mg / L palladium, 30 ml / L sulfuric acid, activation time 10 min, temperature 60~80℃, to form a layer of metallic palladium on the tungsten metal surface;

[0138] 10. Double water rinse: Perform an overflow double water rinse to remove residual palladium activation solution from the surface of the workpiece;

[0139] 11. Inhibition: Inhibition is to remove palladium ions that are difficult to wash off the ceramic surface of the workpiece by water, and to prevent plating penetration. The workpiece is placed in the inhibition solution Shangcun Industrial MPD-BW, 100ml / L, at a temperature of 80℃ for 10min.

[0140] 12. Double water rinse: Perform an overflow double water rinse to remove residual inhibitory solution from the workpiece surface;

[0141] 13. Electroless nickel-boron plating: Immerse the workpiece in an electroless nickel-boron plating solution (BEL-18, 60 ml / L) at 65°C for 30 minutes.

[0142] 14. Double water rinse: Perform an overflow double water rinse to remove residual chemical nickel plating solution from the surface of the workpiece;

[0143] 15. Palladium pre-plating: Immerse the workpiece in a chemical pre-plating palladium solution of PD-30-MW 25ml / L, TPD-30-C 37.5ml / L, and dichlorotetraamminepalladium 0.6g / L at 90℃ for 5 minutes.

[0144] 16. Electroless palladium plating: Immerse the workpiece in an electroless palladium plating solution of TPD-30-MW 100ml / L, TPD-30-C 150ml / L, and dichlorotetraamminepalladium 0.6g / L at 50℃ for 10 minutes.

[0145] 17. Double water rinse: Perform an overflow double water rinse to remove residual chemical palladium plating solution from the surface of the workpiece;

[0146] 18. Chemical gold plating: Immerse the workpiece in a chemical gold plating solution of TWX-40-M10 100ml / L, KCN 50ppm / L, KAuCN 1.0g / L at 80℃ for 30 minutes.

[0147] 19. Double water rinse: Perform an overflow double water rinse to remove residual chemical gold plating solution from the surface of the workpiece;

[0148] 20. Ultrasonic water washing: Ultrasonic water washing is used to better remove residual solution from the surface of the workpiece;

[0149] 21. Drying: Dry at 90℃.

[0150] Result: The resulting workpiece exhibited plating creep, such as... Figure 2 As shown.

[0151] Comparative Example 3

[0152] This comparative example is based on Example 2, except that step "11, Suppression" is omitted, and the rest is the same as Example 2;

[0153] Result: The resulting workpiece exhibited severe plating creep, such as... Figure 3 As shown.

[0154] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate, characterized in that, Includes the following steps: (1) Hanging: Hanging the workpiece to be processed; (2) Degreasing: Degreasing is performed by adding a degreasing agent; (3) Double water wash: Perform overflow double water wash to remove residual pretreatment solution from the surface of the workpiece; (4) Micro-etching: The workpiece is placed in a micro-etching solution for micro-etching; (5) Double water wash: Perform overflow double water wash to remove residual micro-etching solution from the surface of the workpiece; (6) Glass micro-etching: The workpiece is placed in NH4HF2 solution for glass micro-etching; (7) Double water wash: Perform overflow double water wash to remove residual glass micro-etching solution from the surface of the workpiece; (8) Pickling: Immerse the workpiece in the pickling solution for pickling; (9) Palladium activation: Palladium activator is used to activate the tungsten metal and form a layer of metallic palladium on the surface of the tungsten metal; (10) Double water wash: Perform overflow double water wash to remove residual palladium activation solution from the surface of the workpiece; (11) Inhibition treatment: The workpiece is placed in an inhibition solution for inhibition treatment; the inhibition treatment is to remove palladium ions that are difficult to wash off the ceramic surface of the workpiece by water, and to prevent plating penetration. (12) Double water wash: Perform overflow double water wash to remove residual inhibitory solution from the surface of the workpiece; (13) Electroless nickel-boron plating: The workpiece is placed in an electroless nickel-boron solution for electroless nickel-boron plating; (14) Double water rinse: Perform overflow double water rinse to remove residual chemical nickel plating solution from the surface of the workpiece; (15) Palladium pre-plating: The workpiece is placed in a chemical palladium pre-plating solution for palladium pre-plating; (16) Electroless palladium plating: The workpiece is placed in an electroless palladium plating solution for electroless palladium plating; (17) Double water wash: Perform overflow double water wash to remove residual chemical palladium plating solution from the surface of the workpiece; (18) Chemical gold plating: The workpiece is placed in a chemical gold plating solution for chemical gold plating; (19) Double water rinse: Perform overflow double water rinse to remove residual chemical gold plating solution from the surface of the workpiece; (20) Wash with water; (21) Drying.

2. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (1), polytetrafluoroethylene hangers are used for hanging to prevent plating solution from depositing.

3. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (2), the concentration of the degreasing agent is 45-55 g / L, the degreasing temperature is 45-55℃, and the degreasing time is 5-10 min.

4. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (4), the concentration of the micro-etching solution is 300-500 ml / L, the micro-etching temperature is RT~80℃, and the micro-etching time is 20s~30min, wherein RT is room temperature.

5. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (6), the concentration of the NH4HF2 solution is 10g to 50g / L, the glass micro-etching temperature is RT, and the glass micro-etching time is 5 to 10min, wherein RT is room temperature.

6. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (8), the pickling solution is an HCl solution of 300-800 ml / L, the pickling temperature is RT, and the pickling time is 5-10 min, wherein RT is room temperature.

7. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (9), the palladium activator used is: palladium 10-30 mg / L, hydrochloric acid 10-30 ml / L, activation time 3-10 min, and activation temperature 60-80℃.

8. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (9), the concentration of the inhibition solution is 100-150 ml / L, the inhibition treatment temperature is 60-80℃, and the inhibition treatment time is 5-10 min.

9. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (13), the concentration of the chemical nickel boron solution is 60-65 ml / L, the treatment temperature is 60-65℃, and the treatment time is 10-30 min.

10. The method for electroless nickel-palladium-gold plating on a high-temperature co-fired alumina ceramic substrate according to claim 1, characterized in that: In step (15), the chemical composition of the pre-plating palladium solution is TPD-30-MW: 25-30 ml / L, TPD-30-C: 35-40 ml / L, dichlorotetraamminepalladium: 0.6 g-0.7 g / L, the temperature is 70-90℃, and the time is 1-5 min; in step (16), the chemical composition of the pre-plating palladium solution is TPD-30-MW: 100-120 ml / L, TPD-30-C: 150-200 ml / L, dichlorotetraamminepalladium: 0.6-0.7 g / L, the temperature is 40-50℃, and the time is 4-10 min; in step (19), the chemical composition of the pre-plating gold solution is TWX-40-M10: 100-120 ml / L, KCN: 50-60 ppm / L, KAuCN: 1.0~1.2g / L, temperature 70~80℃, time 10~30min.

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